Lower alkyl tertiary butyl ethers, such as methyl tertiary butyl ether (MTBE) and/or ethyl tertiary butyl ether (ETBE) may be added to gasoline as an oxygenate. Such ethers are relatively low volatility components which may be used to improve the octane rating of gasoline.
These ethers may be produced from methanol. A common process for the production of methanol is steam reformation. According to this process, methane is reacted with steam at high temperatures and pressures. Traditionally, natural gas is used as a source of methane. Pursuant to this process, less than 85% of the natural gas is converted to methanol. The remainder of the natural gas is used as fuel for the process. One disadvantage of the steam reformation process is that it utilizes a valuable commercial product, namely natural gas, to produce methanol. A further disadvantage of steam reformation is that it results in the release of substantial quantities of green house gases.
An alternate route for the production of methanol is the Texaco gasification process. According to this process, a hydrocarbon feedstock, such as natural gas, is subjected to partial oxidation with pure oxygen to produce carbon monoxide and hydrogen. The oxygen is obtained from a cryogenic plant. Subsequently, carbon monoxide and oxygen are fed in stoichiometric proportions to a methanol synthesizer.
As a further alternative, a heavy oil distillate, of low value, can be used as a feedstock to the partial oxidation process to put the oil to higher value uses. The molar ratio of carbon monoxide and hydrogen in the resulting feedstock to the methanol synthesizer is approximately one to two. The required molar ratio is one to four to affect methanol synthesis. Accordingly, the mixture of carbon monoxide and hydrogen is subjected to a water shift process which converts approximately half of the carbon monoxide, that is the carbon derived from the feedstock oil and the oxygen derived from the cryogenic separation to carbon dioxide. Subsequently, the carbon dioxide must be separated from the feed stream requiring extensive and costly capital equipment and ongoing operating expense. Subsequently, carbon monoxide and hydrogen in the appropriate stoichiometric proportions are fed to a reactor to produce methanol. One disadvantage with this process is that a cryogenic plant is required to produce oxygen for the partial oxidation reaction. A further disadvantage of this process is that the water shift reaction is required to obtain stoichiometric amounts of carbon monoxide and hydrogen for the methanol synthesizer. Further, in this process, substantially half of the carbon monoxide i.e. carbon and oxygen are converted to carbon dioxide which is of no further contribution to this process. The high level of carbon dioxide, a greenhouse gas, produced effectively negates the environmentally beneficial aspect of utilizing methanol fuels and is a very considerable waste of usable energy. Accordingly, the use of low value heavy oil, which is abundant, is not cost competitive with higher value natural gas consumption.